This invention relates to a feed screw device of a ball screw, square thread, etc. Particularly, the invention relates to a feed screw device that can automatically supply a lubricant over a long term.
A conventional ball screw, a kind of feed screw device, is described in Japanese Utility Model Unexamined Publication Nos. Hei 7-4952 and 6-47762, etc., for example.
This kind of ball screw comprises a spiral thread groove 50a made in the outer peripheral surface of a screw shaft 50 threadably engaging a spiral thread groove 51a made in the inner peripheral surface of a nut member 51 via a plurality of balls 52, as shown in FIG. 1, for converting relative rotation of the screw shaft 50 to the nut member 51 into relative displacement in an axial direction of the nut member 51 via the balls 52.
An annular recess 53 is formed in both end parts of the inner diameter face of the nut member 51 (in FIG. 1, only the right end is shown), and a sealing member 54 is mounted on the recess 53.
The sealing member 54 is made from plastic containing a lubricant into a ring shape, and a projection 54a that can be fitted into the thread groove 50a of the screw shaft 50 projects from the inner peripheral surface of the sealing member.
A ring-like garter spring 55 is inserted in the circumferential direction between the outer peripheral surface of the sealing member 54 and the recess 53 of the nut member 51. The garter spring 55 clamps down all the outer peripheral surface of the sealing member 54 toward the outer peripheral surface of the screw shaft 50, that is, the sealing member 54 is pressed in the inner diameter direction.
Further, a tapped hole 56 radially penetrating the circumferential wall of the nut member 51 is made in the position of the recess 53 in the nut member 51 and a set screw 57 is fitted into the tapped hole 56, thereby fixing the sealing member 54 to the nut member 51.
The garter spring 55 sets the gap between the inner peripheral surface of the sealing member 54 and the outer peripheral surface of the screw shaft 50 to zero or less for preventing the lubricant filled in the ball screw from leaking to the outside and a foreign material from entering the ball screw from the outside.
Further, the lubricant exuding from the sealing member 54 decreases frictional resistance of the slide portion between the inner peripheral surface of the sealing member 54 and the outer peripheral surface of the screw shaft 50, namely, slide torque and at the same time, is supplied to the thread groove 50a of the screw shaft 50, the balls 52, and the thread groove 51a of the nut member 51.
However, for the conventional feed screw device of the structure as described above, the garter spring 55 needs to be inserted between the outer periphery of the sealing member 54 and the recess 53 of the screw shaft 50 so that a dimension error of the sealing member 54 is absorbed and that the inner peripheral surface of the sealing member 54 comes in sliding contact with the outer peripheral surface of the screw shaft 50; it is feared that the outer diameter of the feed screw device may grow as large as the garter spring.
In the conventional structure, the sealing member 54 is pressed diametrically, so that it is abutted against the outer peripheral surface of the screw shaft 50, thus the spring needs to be disposed on all the outer periphery of the sealing member 54 in the circumferential direction.
The inner diameter portion on the opposite side (portion not pressed by the garter sprint) to the side pressed by the garter spring 55 of the sealing member 54 in the axial direction apts to float-up with respect to the outer peripheral surface of the screw shaft and it is feared that a sufficient lubricant will not be supplied from the portion.
Some conventional feed screw devices comprise a spring inserted between the tip of the set screw 57 and the sealing member 54 in place of the garter spring 55. However, the lubricant supply section is also pressed only diametrically, thus it is feared that the inner peripheral surface of the sealing member 54 may be placed out of contact with the outer peripheral surface of the screw shaft 50 or that the portion pressed by the set screw in sliding contact with the screw shaft may be worn on one side in portions shifted 90 degrees from the placement position of the set screw 57, etc., for example.
Even if hardware for suppressing jump out of the sealing member 54 from the recess 53 is attached to the nut member 51, the tapped hole 56 needs to be made in the nut member 51 and fixed by the set screw 57 to prevent accompanying rotation of the screw shaft 50 of the sealing member 54 in addition to the hardware; workability is poor.
Further, when the sealing member 54 has a part cut (for example, the sealing member 54 is made into c-shaped) because of attachment thereof, the inner peripheral surface of the sealing member 54 does not come in sufficient contact with the screw shaft 50 and it is feared that a sufficient lubricant will not be supplied from the sealing member 54 depending on the operating condition.
Known as another ball screw, a kind of conventional feed screw device, is a device wherein a space 204 between a screw shaft 201 and a ball screw nut 202 threadably engaged into the screw shaft 201 via a large number of balls 203 is filled with grease or lubricant, as shown in FIG. 2. The ball screw is of seal type wherein an annular recess 205 is made in an end of the ball screw nut 202 and a sealing member 206 is fitted into the annular recess 205 to prevent powder dust, etc., from entering into the ball screw nut 202.
By the way, to lubricate such a conventional ball screw device, normally grease or lubricant is supplied from a grease nipple 207 attached to the ball screw nut 202 to a ball circulation passage for lubricating a rolling element.
However, particularly when the ball screw device adopting such a lubrication system directly using lubricant or grease is used in a high-temperature environment or a environment wherein wood chips, etc., easily absorbing lubricants are existed, the filled lubricant or grease flows out to the outside, is exhausted fast, and must be again supplied repeatedly for a short term. Japanese Utility Model Unexamined Publication No. Hei 7-4952 is known as application relating to an oil-containing polymer lubrication ball screw to improve this point.
For the oil-containing polymer lubrication ball screw disclosed here, a lubricant supply member mounted on a ball screw nut is formed of lubricant-containing rubber or synthetic resin and the lubricant continuously exuding from the lubricant supply member is automatically supplied to a rolling element lubrication passage of the ball screw nut.
However, with the ball screw, as the lubricant supply member containing the lubricant runs with the ball screw nut while coming in contact with the screw shaft, the lubricant exudes from the contact part for lubrication; lubricant supplied to a guide rail is easily absorbed particularly in an environment wherein foreign materials such as wood chips easily absorbing lubricant are existed, and the lubricant can also be absorbed from the lubricant-containing polymer member; resultantly, it is feared that a lubrication failure may be invited.
It is therefore an object of the invention to provide a feed screw device for enabling a lubricant-containing member to come in uniform contact with an outer peripheral surface of a screw shaft without enlarging the outer diameter of the feed screw device and in a simple structure.
According to the invention, there is provided a feed screw device comprising a screw shaft, a nut member threadably engaging an outer periphery of the screw shaft, and a lubricant supply device being fixed to the nut member, coming in contact with the outer peripheral surface of the screw shaft, and having a predetermined elastic force, wherein at least the portion of the lubricant supply device facing the screw shaft is rubber or synthetic resin containing a lubricant, wherein a notch is made in the outer periphery of the lubricant supply device, and wherein an expansion member fitted at least with the notch pressed in the circumferential direction of the lubricant supply device is inserted into the notch.
In the structure, when the expansion member is inserted into the notch of the lubricant supply device, it causes the notch to push and widen at least the outer periphery of the lubricant supply device in the circumferential direction.
Thus, a compression force along the circumferential direction acts on the inside of the outer periphery of the lubricant supply device, at least deforming all the inner peripheral surface in the inner diameter direction. Resultantly, the inner diameter of the lubricant supply device is reduced for absorbing a dimension error of the lubricant supply device, and the inner peripheral surface of the lubricant supply device comes in contact with the outer peripheral surface of the screw member.
As the feed screw device is driven, a lubricant contained in the lubricant supply device exudes gradually over time, whereby slide resistance between the outer peripheral surface of the screw member and the inner peripheral surface of the lubricant supply device is decreased and as the feed screw device is driven, a lubricant is supplied to the outer peripheral surface of the screw member.
In the feed screw device according to the present invention, all the inner peripheral surface of the lubricant supply device can be brought into contact with the outer peripheral surface of the screw shaft by only inserting the expansion member into a part of the lubricant supply device (notch), so that any member, such as a garter spring to be installed on all the outer peripheral surface of the lubricant supply device which was needed by the conventional lubricant supply device can be eliminated.
In the case where the expansion member is formed with a projection which is projected from a part of the outer peripheral surface of the lubricant supply device and is fitted into a part of the nut member, etc., it is possible that the expansion member also serves prevention of rotation of the lubricant supply device.
In addition, according to the invention, there is provided in a screw transmission device comprising a screw shaft, a nut member threadably engaging an outer periphery of the screw shaft, and a ring-like lubricant supply device being disposed in the nut member with one axial end face opposed axially to the nut member and an inner peripheral surface opposed to an outer peripheral surface of the screw shaft, wherein at least the portion of the lubricant supply device facing the screw shaft is rubber or synthetic resin containing a lubricant, the improvement which comprises a press member having a portion opposed axially to an axial opposed end face of the lubricant supply device and being fixed to the nut member and a projection projecting from the press member to the lubricant supply device and inserted into the lubricant supply device.
Further, in the screw transmission device, at least two projections can also be provided and inserted into the lubricant supply device so that pilot pressure in the circumferential direction is put on the lubricant supply device as load.
In the structure, the device is sandwiched between the press member and the nut member, so that an axial movement of the lubricant supply device relative to the nut member is restricted and the projection projecting from the press member prevents the lubricant supply device from rotating with the screw shaft.
That is, an axial movement and rotation of the lubricant supply device can be prevented by only fitting the press member having the projection.
As the screw transmission device is driven, a lubricant contained in the lubricant supply device exudes gradually over time, so that slide resistance between the outer peripheral surface of the screw member and the inner peripheral surface of the lubricant supply device is decreased and as the screw transmission device is driven, a lubricant is supplied to the outer peripheral surface of the screw member.
Here, a pair of the projections may be provided approaching each other and the projection span may be set smaller than the span between the paired projection insertion positions disposed in the lubricant supply device. In doing so, by sandwiching between the paired projections, pilot pressure in the circumferential direction is put as load and such a force to hold down the screw shaft acts on the inner peripheral surface of the lubricant supply device.
Further, it is another object of the invention to provide a long-life feed screw device stable over a long term by automatically replenishing a lubricant supply member with a lubricant for suppressing occurrence of a lubrication failure.
To the end, according to a second aspect of the invention, there is provided, in a feed screw device comprising a screw shaft, a screw nut threadably engaging an outer periphery of the screw shaft, and a lubricant supply device being disposed at both ends of the screw nut for sealing the gap opening between the screw nut and the screw shaft, the improvement wherein the lubricant supply member is made of a lubricant-containing polymer member, the lubricant-containing polymer member being formed with lubricant reserve parts.
According to invention, the lubricant-containing polymer member seals both the ends of the screw nut and shuts off the inside of the screw nut from the external atmosphere, whereby even if the feed screw device is used in the external atmosphere which is of a bad environment wherein wood chips, etc., easily absorbing lubricant are existed, the inside of the screw nut is protected against the wood chips, etc., and the smooth lubrication effect can be maintained over a long time.
As a lubricant exudes from the lubricant-containing polymer member and is consumed, the lubricant-containing polymer member is replenished with a new lubricant sealed in the lubricant reserve parts, so that the lubricant exudes from the lubricant-containing polymer member over a long time even in atmosphere wherein wood chips, etc., easily absorb the lubricant supplied to a guide rail, so that stable lubrication can be carried out for a long time.
If foreign materials such as wood chips are deposited on the lubricant-containing polymer member and the lubricant is absorbed from the portion, the lubricant-containing polymer member is replenished with a lubricant from the lubricant reserve parts, thus it is not feared that a lubrication failure will be invited.
Specifically, the lubricant reserve parts formed in the lubricant supply device may be lubricant reserve holes made near the sealed face of the screw shaft or a lubricant reserve peripheral groove extending surrounding the screw shaft. If an annular recess is made in the screw nut and the lubricant supply member is fitted into the annular recess and the lubricant reserve holes or the lubricant reserve peripheral groove is closed on the inner peripheral surface or bottom face of the recess, a lubricant filled in the lubricant reserve holes or the lubricant reserve peripheral groove can be sealed by a simple structure.
If the lubricant reserve peripheral groove is formed, the lubricant-containing polymer member is replenished uniformly with a new lubricant sealed in the lubricant reserve peripheral groove, thus stable lubrication can be carried out for a long time. If a plurality of the lubricant reserve holes are made in the circumferential direction surrounding the screw shaft, the lubricant-containing polymer member is replenished uniformly with a new lubricant in the lubricant reserve holes, thus stable lubrication can be carried out for a long time.
If a reinforcing plate is disposed overlapping the lubricant-containing polymer member so as to shut off the lubricant-containing polymer member from the external atmosphere, it prevents wood chips, dust, etc., from coming in contact with the lubricant-containing polymer member, so that absorbing the lubricant in wood chips, dust, etc., from the portion can be prevented. If a reinforcing plate is disposed so that a compression force acts on the lubricant-containing polymer member, the lubricant-containing polymer member can be adjusted in hardness and insufficient strength by the reinforcing plate, and breakage, cracks, etc., of the lubricant-containing polymer member can be prevented. Since the reinforcing plate is provided, a metal reinforcing plate (mandrel) need not be used; a problem of adhesion between the lubricant-containing polymer member containing a large amount of lubricant and the metal reinforcing plate need not be considered.
Further, if the lubricant-containing polymer member is formed with communication holes from the lubricant reserve parts (lubricant reserve holes, lubricant reserve peripheral groove) to the face coming in contact with the screw shaft, the lubricant sealed in the lubricant reserve parts flows out into the screw shaft through the communication holes. Thus, an appropriate lubricant-containing polymer member is provided for a device requiring a large amount of lubricant.
For example, a lubricant-containing polymer member can be adopted as the lubricant supply device containing a lubricant according to the invention.
For example, the product manufactured in the following manner can be used as the lubricant-containing polymer member: Any of paraffin hydrocarbon oil such as polyolefin oil, naphthene hydrocarbon oil, mineral oil, ether oil such as dialkyl diphenyl ether oil, or ester oil such as phthalate ester or trimellitate is mixed as a lubricant with a polymer selected from the group consisting of polyolefin polymers basically having the same chemical structure such as polyethylene, polypropylene, and polymethylpentane and the mixture is fused, then poured into a predetermined mold and cooled and fixed under pressure.
Various additive agents such as an antioxidant, a rust preventive, a wear inhibitor, a defoaming agent, and an extreme pressure agent may be previously added to the mixture.
The percentage composition of the lubricant-containing polymer member may be set to 20%-80% by weight of polyolefin polymer and 80%-20% by weight of lubricant with respect to all weight, because if the polyolefin polymer is less than 20% by weight, hardness, strength, etc., required as the lubricant supply device cannot be provided and if the polyolefin polymer exceeds 80% by weight (the lubricant is less than 20% by weight), lubricant supply lessens and the slide torque reduction and lubricant supply effects decrease.
The above-mentioned polymers have the same basic structure and differ in average molecular weight, covering the range of 1xc3x97103 to 5xc3x97106. Among the polymers, those of comparatively low molecular weight ranging from 1xc3x97103 to 5xc3x97105and those of ultra high molecular weight ranging from 1xc3x97106 to 5xc3x97106 are used solely or mixed as required.
To improve the mechanical strength of the lubricant supply device, the following thermoplastic resin and thermosetting resin may be added to the polyolefin polymer:
Resin such as polyamide, polycarbonate, polybutylene terephthalate, polyphenylene sulfide, polyether sulfone, polyether ether ketone, polyamide imide, polystyrene, or ABS resin can be used as the thermoplastic resin.
Resin such as unsaturated polyester resin, urea resin, melamine resin, phenol resin, polyimide resin, or epoxy resin can be used as the thermosetting resin.
The resins may be used solely or mixed.
Further, to disperse the polyolefin polymer and any other resin in a more uniform state, a proper compatibilization agent may be added as required.
In addition to the polyolefin polymer and lubricant combinations as described above, polyurethane rubber cured in a grease-containing condition can also be used as the lubricant-containing polymer, as described below in detail:
Polyurethane rubber is a compound produced by reaction of polyisocyanate with an activated hydrogen compound.
Tolylene diisocyanate (TDI), hexamethylene diisocyanate (MDI), prepolymer (MW1000-MW2000) produced by reaction of TDI and MDI with an activated hydrogen compound, such as castor oil, or the like can be used as polyisocyanate.
A long chain activated hydrogen compound such as hydrocarbon of polybutadiene, etc., polyether of polyoxypropylene, etc., caster oil or caster oil series polyol, polyester, or polycarbonate, a polyhydroxy compound such as water or ethylene glycol, or a short chain activated hydrogen compound such as amino alcohol, or polyamino compound can be used as the activated hydrogen compound.
Normal grease such as mineral oil or lithium soap grease can be used as the grease.
In this case, preferably the percentage composition of the lubricant-containing polymer member may be set to 80%-40% by weight of polyurethane rubber and 20%-60% by weight of grease with respect to all weight. If polyurethane rubber is less than 40% by weight, necessary hardness, strength, etc., cannot be provided.
If polyurethane rubber exceeds 80% by weight (grease is less than 20% by weight), lubricant supply lessens and the slide torque reduction effect decreases.